System and method for manufacturing a dental prosthesis and a dental prosthesis manufactured thereby

ABSTRACT

A dental prosthesis is made by externally machining successive layers of wax, each of which is formed on a previous prosthesis layer and/or on a coping. Each wax layer is used to form a mold in situ over the previous prosthesis layer/coping, and the appropriate prosthesis material is cast or otherwise molded to conform to the wax layer by the mold.

CROSS-REFERENCE

This application is a continuation application of U.S. patentapplication Ser. No. 16/041,532, filed Jul. 20, 2018, which is acontinuation application of U.S. patent application Ser. No. 14/533,033,filed Nov. 4, 2014, now U.S. Pat. No. 10,059,059, issued Aug. 28, 2018,which is a continuation application of U.S. patent application Ser. No.12/659,385, filed Mar. 8, 2010, now U.S. Pat. No. 8,909,363, issued Dec.9, 2014, which is a continuation application of U.S. patent applicationSer. No. 11/783,149, filed Apr. 6, 2007, now U.S. Pat. No. 7,689,310,issued Mar. 30, 2010, which is a continuation application of U.S. patentapplication Ser. No. 11/290,449, filed Dec. 1, 2005, now U.S. Pat. No.7,236,842, issued Jun. 26, 2007, claiming the benefit under 35 U.S.C.119(e) of U.S. Provisional Patent Application No. 60/632,350, filed Dec.2, 2004, the contents of each of which are hereby incorporated byreference in their entireties.

FIELD OF INVENTION

This invention relates to teeth restoration, specifically to a systemand method for fabricating dental prostheses, and to dental prosthesesmade thereby.

BACKGROUND OF THE INVENTION

The manufacture of dental prostheses such as crowns and bridges needs tobe as precise as possible in order to ensure that, externally, theprosthesis fits within the area of the oral cavity assigned thereto,while also fitting properly onto the preparation. At the same time, itmay sometimes be desired to have a number of layers in order to providethe prosthesis with a natural-looking appearance, in which inner layersmay be more opaque than outer layers, for example, or contain amosaicing of differently colored patches, and/or wherein each layer maybe made from a different material.

Manual manufacturing methods for dental prostheses typically require anumber of “fitting and fixing” cycles in order to ensure that the crownis properly dimensioned before finally fixing the prosthesis to thepreparation in the intraoral cavity.

CNC-based methods for manufacturing dental prostheses are known andrepresent a significant improvement in automating the manufacturingprocess to provide a high degree of dimensional accuracy. For example,in U.S. Pat. No. 4,663,720 and in U.S. Pat. No. 5,027,281, material isremoved from a massive block of material by means of a CNC millingmachine, and the machining paths are calculated from a 3D numericalmodel of prosthesis. In U.S. Pat. No. 4,937,928, a dental prosthesis ismanufactured by successively applying a number of layers of prosthesismaterial on a model in the shape of the part of the teeth where theprosthesis is to be provided. After each layer is applied, the workpieceis worked by a CNC tool controlled by a CAD/CAM system. In U.S. Pat. No.5,378,154, a similar method is used for forming layers of material ontoa preparation, machining each layer along paths that follow threedimensional irregularly spaced curved lines.

SUMMARY OF THE INVENTION

The present invention is directed to a method for manufacturing a dentalprosthesis, comprising:

(a) providing at least one coping adapted for implantation at a dentalsite, the or each said at least one coping having a correspondingexternal surface;

(b) providing a three-dimensional (3D) virtual model of said dentalprosthesis having at least one virtual internal surface, the or eachsaid at least one virtual internal surface being substantiallycomplementary to a corresponding said external surface of the or eachsaid coping, respectively;

(c) generating computerized numerical control (CNC) instructionscorresponding to said 3D model;

(d) producing a set of wax models, comprising at least one wax model,corresponding to said prosthesis in association with said at least onecoping by means of material removal operations based on said CNCinstructions;

(e) producing a dental prosthesis on said coping from said set of waxmodels.

The method may be applied for the fabrication of a single layered crownprosthesis, wherein said set of wax models comprises a wax model of saidprosthesis substantially corresponding to said 3D virtual model.Alternatively, the method may be applied for the fabrication of amulti-layered crown prosthesis, wherein said set of wax models comprisesa wax model of each layer of said prosthesis substantially correspondingto virtual layers created in said 3D virtual model.

Alternatively, the method may be applied for the fabrication of a singlelayered bridge prosthesis, wherein said set of wax models comprises awax model of said prosthesis substantially corresponding to said 3Dvirtual model. Alternatively, the method may be applied for thefabrication of a multi-layered bridge prosthesis, wherein said set ofwax models comprises a wax model of each layer of said prosthesissubstantially corresponding to virtual layers created in said 3D virtualmodel. In such cases, said 3D virtual model comprises two said virtualinternal surfaces, each substantially complementary to a correspondingsaid external surface of one or another of two said copings.

Step (a) may be performed using a lost wax process, or via a directmachining process, for example.

Typically, step (b) comprises providing a three-dimensional (3D) digitaldata relating to the patient's dentition, said 3D data including datarepresentative of the surface topology of said preparation and itssurroundings. Step (b) may be performed using a suitable opticalscanner, such as for example comprises a probe for determining threedimensional structure by confocal focusing of an array of light beams,and typically performed directly on the intraoral cavity comprising saidpreparation. Alternatively the digital data of step (b) is obtained froma virtual model of a prosthesis designed for said preparation.Typically, in step (b) an external surface of the virtual model iscreated based on predetermined criteria, which may relate for example toproviding adequate mechanical strength for the prosthesis, and/or toproviding a natural-looking appearance to the prosthesis.

Step (e) may be carried out according to a lost wax process, and thedental prosthesis may be made from a suitable metal and/or from asuitable ceramic material.

When the prosthesis comprises a plurality of layers, the set of waxmodels comprises a corresponding plurality of wax models, an innermostsaid wax model being formed with respect to said at least one coping,and successive wax models being formed in turn on a previously formedlayer of the prosthesis based on a corresponding said wax model.

The present invention also relates to a dental prosthesis, fabricatedaccording to the method of the invention.

The present invention is also directed to a method for the fabricationof a set of wax models, comprising at least one wax model, to be usedfor the fabrication of a dental prosthesis of at least one tooth to befitted over at least one tooth preparation, comprising:

(a) providing at least one coping adapted for implantation at a dentalsite, the or each said at least one coping having a correspondingexternal surface;

(b) providing a three-dimensional (3D) virtual model of said dentalprosthesis having at least one virtual internal surface, the or eachsaid at least one virtual internal surface being substantiallycomplementary to a corresponding said external surface of the or eachsaid coping, respectively;

(c) generating computerized numerical control (CNC) instructionscorresponding to said 3D model;

(d) producing a set of wax models, comprising at least one wax model,corresponding to said prosthesis in association with said at least onecoping by means of material removal operations based on said CNCinstructions.

The present invention also relates to a set of wax models, fabricatedaccording to the method of the invention.

The present invention is also directed to a system for manufacturing adental prosthesis, comprising:

(a) first fabricating system for providing at least one coping adaptedfor implantation at a dental site, the or each said at least one copinghaving a corresponding external surface;

(b) first computer based system for providing a three-dimensional (3D)virtual model of said dental prosthesis having at least one virtualinternal surface, the or each said at least one virtual internal surfacebeing substantially complementary to a corresponding said externalsurface of the or each said coping, respectively;

(c) second computer based system for generating computerized numericalcontrol (CNC) instructions corresponding to said 3D model;

(d) second fabricating system for producing a set of wax models,comprising at least one wax model, corresponding to said prosthesis inassociation with said at least one coping by means of material removaloperations based on said CNC instructions;

(e) third fabricating system for producing a dental prosthesis on saidcoping from said set of wax models.

Optionally, the first and second computer systems may be integrated ormay be the same computer system, or alternatively they may comprisedifferent systems. Optionally, the first and second, or the first andthird, or the second and third, or the first and second and thirdfabricating systems may be integrated or may be the same fabricatingsystem, or alternatively they may comprise different systems.

The present invention is also directed to a system for the fabricationof a set of wax models, comprising at least one wax model, to be usedfor the fabrication of a dental prosthesis of at least one tooth to befitted over at least one tooth preparation, comprising:

(a) first fabricating system for providing at least one coping adaptedfor implantation at a dental site, the or each said at least one copinghaving a corresponding external surface;

(b) first computer based system for providing a three-dimensional (3D)virtual model of said dental prosthesis having at least one virtualinternal surface, the or each said at least one virtual internal surfacebeing substantially complementary to a corresponding said externalsurface of the or each said coping, respectively;

(c) second computer based system for generating computerized numericalcontrol (CNC) instructions corresponding to said 3D model;

(d) second fabricating system for producing a set of wax models,comprising at least one wax model, corresponding to said prosthesis inassociation with said at least one coping by means of material removaloperations based on said CNC instructions.

Optionally, the first and second computer systems may be integrated orcomprise the same computer system, or alternatively they may bedifferent systems. Optionally, the first and second fabricating systemsmay be integrated or may be the same fabricating system, oralternatively they may comprise different systems.

In each aspect of the invention outlined above, step (d) involvesproviding a set of wax models, comprising at least one wax model,corresponding to the prosthesis in association with the at least onecoping by means of material removal operations based on said CNCinstructions. Step (d) may be executed by any suitable material removaloperation, for example each successive wax model may be machined (forexample by milling) from an external layer of wax that is deposited onthe previous prosthesis layer, which may be the coping itself.

The term “prosthesis” is herein taken to include onlays, such as crownsand bridges, for example, and inlays, such as caps, for example, and anyother artificial partial or complete denture. Generally, where one ormore copings are used, the term “prosthesis” is used herein to refer tothe artificial structure replacing a dental structure, and excluding theone or more copings.

The terms “tool” and “machining tool” are taken herein to include anytool that is adapted for material removal, and may include inter aliamechanical tools such as drills for example, laser tools such as forexample laser drills or cutters, ultrasonic tools such as for exampleultrasonic cutters, and so on. Preferably, the machining paths andmaterial removal characteristics of such tools can be finely controlled,typically by computer means.

The term “layer” is used herein to a thickness of material partially orfully overlying a coping, as well as to a thickness of material that maybe partially or fully overlying or underlying another layer of material.

Herein, “dental material” refers to any material associated with dentalstructures of the intra oral cavity, including but limited to naturaldental materials such as for example enamel, dentine, pulp, dentalroots, and non-natural dental materials such as for example metallic andnon-metallic filings, restorations, crowns, bridges, copings,preparations, and so on.

Herein, “dental clinic” refers to the interface between a dentalpractitioner and a patient, and thus includes any physical entity, inparticular a clinic, in which there is interaction between a dentalpatient and a dental practitioner. While “dental practitioner” and “careprovider” typically refer herein to a dentist, doctor or dentaltechnician, it also includes herein all other caregivers that mayinteract with a dental patient during the course of a dental treatment.While “dental patient” or “patient” typically refer to a personrequiring the dental services of a dental practitioner, it also includesherein any person regarding whom it is desired to create a 3D numericalmodel of the intra oral cavity thereof, for example for the purpose ofpracticing the same or for carrying out research.

The term “dental site” is herein taken to include any part of theintraoral cavity in which it is desired to implant a dental prosthesis,and includes, for example, the area vacated by one or more teeth such asto expose one or more preparations and/or one or more artificial pivotsor the like to enable a crown or bridge prosthesis to be fitted thereat.Dental site also includes teeth in which some dental material has beenremoved and are to receive a restoration including onlays, inlays, andany other artificial partial or complete denture.

While the term “preparation” typically refers to the stump (includingthe finish line and shoulder) that is left of the tooth that is to bereplaced by the prosthesis—typically a crown or bridge—and on which theprosthesis is to be mounted, the term herein also includes implants suchas for example artificial stumps, pivots, cores and posts, or otherdevices that may be implanted in the intraoral cavity forming a basisfor implanting the prosthesis.

The term “prosthodontic procedure” refers, inter alia, to any procedureinvolving the intraoral cavity and directed to the design, manufactureor installation of a dental prosthesis at a dental site within theintraoral cavity, or a real or virtual model thereof, or directed to thedesign and preparation of the dental site to receive such a prosthesis.

The term “numerical entity” is used herein synonymously with virtualmodel, 3D model, and other such terms, and relates to a virtualrepresentation of a real object, typically of a dentition or at least apart of intraoral cavity, or of a real model thereof, for example.

The term “dental coping” as used herein refers to a support structurefor a crown, i.e. structure that cups only one tooth, as well as asupport structure for a bridge, i.e. structure that cups more than onetooth. The dental coping may be fabricated from any suitable materials,including but not limited to metal, ceramo-metal materials, ceramics,etc.

The 3D digital data may be obtained by a number of ways known per se.For example, such digital data may be obtained in a manner as describedin WO 00/08415, U.S. Patent Publication No. 2002/0137011 or in any ofU.S. Pat. Nos. 6,099,314 and 6,334,853, or any combination thereof.

The 3D data includes the surface topology of the preparation, as well asits surroundings. Furthermore, such 3D digital data may also compriseother data, for example, data that was added by the orthodontist or adental technician, such as the preparation's finish line.

The present invention provides, in its first aspect, a method and systemfor fabricating a dental prosthesis of at least one tooth which is to befitted over t least one tooth preparation.

By way of example, the coping used in connection with the invention maybe designed primarily on the basis of the surface topology of thepreparation and other factors such as the coping wall's thickness,finish line data, etc.

The generation of the virtual 3D coping data may be automatic, manual ora combination thereof.

The term “wax” includes any material that is relatively hard and lendsitself to machining, particularly milling, while having a sufficientlylow melting point and appropriate kinematic viscosity that renders itsuitable for use in a lost wax process or the like.

The wax that should be used in accordance with the invention is hard anddurable that lends itself to milling in a milling machine. Anotherrequirement of the wax is that after melting, it should have a viscositysufficiently low to be usable in a lost wax technique known per se inthe art of metal casting.

A typical wax that can be used in accordance with the invention is suchhaving a melting point and congealing point of 55-80° C. and a kinematicviscosity of less than 90 m² sec. at about 100° C.

According to the invention, a dental prosthesis may be made byexternally machining successive layers of wax, each of which is formedon a previous prosthesis layer and/or on a coping. Each wax layer isused to form a mold in situ over the previous prosthesis layer/coping,and the appropriate prosthesis material is cast or otherwise molded toconform to the wax layer by the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a flowchart illustrating various steps in a preprocess forgenerating CNC instructions for machining wax layers.

FIG. 2 is a flowchart illustrating various steps in a manufacturingprocess according to the invention.

FIG. 3 schematically illustrates a dental site of an intraoral cavity inwhich it is desired to implant a crown prosthesis.

FIG. 4 schematically illustrates a dental site of an intraoral cavity inwhich it is desired to implant a bridge prosthesis.

FIG. 5 schematically illustrates a system for generating CNCinstructions for machining wax layers.

FIG. 6 illustrates a typical multi-layered 3D virtual model of a crownprosthesis.

FIG. 7 schematically illustrates a system for manufacturing a dentalprosthesis according to the invention.

FIGS. 8a to 8h schematically illustrate various stages employed in themanufacture of a multi-layered crown prosthesis according to theinvention.

FIGS. 9a to 9c schematically illustrate various stages employed in themanufacture of a single-layered crown prosthesis according to theinvention.

FIGS. 10a to 10e schematically illustrate various stages employed in themanufacture of a multi-layered bridge prosthesis according to theinvention.

FIG. 11 illustrates a holder for maintaining the required spatialrelationship between two copings used for manufacturing a bridgeprosthesis

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 schematically illustrate an exemplary implementation ofthe present invention for the fabrication of a dental prosthesis,typically carried out with the aid of a computer system, the operationof which will be explained hereinbelow.

In particular, FIG. 2 illustrates various steps of a process accordingto the invention for fabricating a dental prosthesis, described asfollows in the context of a crown prosthesis, though the method applies,mutatis mutandis, to other prostheses, for example a crown:—

Step 210—a coping is provided, adapted for fitting onto the preparationsat the dental site.

Step 220—a layer of wax is applied to the coping, this layer exceedingthe envelope of the corresponding layer of the crown being fabricated.

Step 230—the wax layer is subjected to a CNC-controlled material removaloperation to provide an outer surface that corresponds to a designedlayer surface for the layer. CNC instructions for the material removaloperation are provided in Step 150.

Step 240—the wax layer is invested in a material that solidifies ontothe external side of the wax layer (still on the coping) and forms amold (this stage is known as the “investment” stage).

Step 250—the combined structure is then heated such that the wax isburnt out, leaving a cavity into which the crown layer may be cast.

Step 260—the crown layer is cast in the mold using a metal, ceramic, orany other suitable material, and the mold material is removed.

Step 270—if this was the last layer required for the crown, Step 290 isimplemented; otherwise, another layer is fabricated on the crown,continuing with Step 280.

Step 280—another layer of wax is applied, this time to the outermostlayer of the crown fabricated so far, and steps 230 to 270 are performedbased on the new wax layer and corresponding CNC instructions providedin step 150.

FIG. 1 illustrates various steps of a pre-process 100 that may be takento provide suitable Computer Numerical Control (CNC) instructions thatare used in step 150 of the process 200 of FIG. 2:—

Step 110—a preparation is formed at the dental site to receive thecoping.

Step 120—a 3D virtual model of the dental site including the preparationis provided.

Step 130—occlusion data, finish line data, shoulder data (whereapplicable) and surface data of the preparation are obtained from thevirtual model.

Step 140—the coping geometry and the geometry of each layer of the crownis designed.

Step 150—Computer Numerical Control instructions for each successivelayer of the crown are prepared from the geometrical data in Step 140.

The above steps are now described in detail, first in the context of acrown prosthesis, and then in the context of a bridge prosthesis.

Referring to Step 110, FIG. 3 shows a section 10 of the intraoral cavityof a patient in which tooth prosthesis in the form of a crown (shown asdotted line 20) is to be fitted over tooth preparation 12, in theillustrated example—in patient's lower jaw. In the example of FIG. 3,the root and base of the missing tooth are sufficiently strong andhealthy, and the care provider prepared the preparation 12 at the dentalsite for the crown typically by removing a portion of the enamel anddentin. If the tooth to be restored is severely decayed or weak, then itmay be necessary to insert a metal implant or pivot (also known as coresor posts) by any one of a number of ways known per se.

According to the present invention, in step 110 a material removaloperation is applied to a part of the intra oral cavity. Such a materialremoval operation may be executed using any suitable machining tool thatis adapted for material removal, and may include inter alia mechanicaltools such as drills for example, laser tools such as for example laserdrills or cutters, ultrasonic tools such as for example ultrasoniccutters, and so on. At least a part of the material removal operationmay comprise in some cases a loss of dental material, occurring, forexample, via disease, mechanical forces such as a blow to the teeth forexample, and so on.

Such a material removal operation is directed for the purpose ofprosthodontic procedures, and thus includes the construction of a dentalpreparation at a dental site, so as to receive a prosthesis such as acrown, for example, or for providing a dental filling or restorationthereat.

FIG. 4 shows another section 10′ of the intraoral cavity of a patient inwhich a bridge prosthesis (shown as dotted line 220) is to be implanted,fitted over a pair of preparations 212, 214 each similar to thepreparation 12 described in connection with FIG. 3.

In Step 120, and referring again to FIG. 3, once the preparation 12 iscompleted, the 3D digitized data W of the intraoral cavity, includingthe dentition and associated anatomical structures of a patient isobtained, and thus suitable equipment for scanning a patient's teeth isused by the care provider to acquire the 3D data. The production of thevirtual 3D working model of the preparation and its surroundings isknown per-se. The 3D digitized data W, herein also referred to as a“virtual model” or “numerical entity” is representative of thethree-dimensional surface of the preparation 12 and the surroundingareas of the intraoral cavity. The said numerical entity W is typicallyat least “three-dimensional”, that is, each data point of the data setcomprises at least three prime independent variables relating to spatialcoordinates of a surface, typically defined along orthogonal Cartesianaxes, x, y, z. Alternatively, these variables may be defined along polaraxes or any other geometric system in which a surface may be described.Thus, the numerical entity W typically comprises a data set having aplurality of at least 3-dimensional arrays—(x, y, and z), wherein eacharray represents the x, y, z, geometrical coordinates.

Any suitable means may be used to provide the numerical entity W. FIG. 5illustrates the main elements of a system 50 for acquiring the 3Dnumerical entity, comprising a suitable scanner 31, a microprocessor orcomputer 52, and a display means 54. According to the invention,digitized three-dimensional (3D) information W of the patient'sintra-oral cavity, or part thereof, 10 is created by the system 50 usingscanner 31. Preferably, the 3D digitized data of the intraoral cavity isobtained, including the dentition and associated anatomical structuresof a patient. The scanning means 31 may include, for example, ahand-held scanner that is used by the practitioner or other user toacquire the 3D data. Advantageously, a probe for determining threedimensional structure by confocal focusing of an array of light beamsmay be used, for example as manufactured under the name of PROSTHOCAD oras disclosed in WO 00/08415, the contents of which are incorporatedherein in their entirety. Such a scanner 31 makes use of confocalimaging for providing an accurate three-dimensional representation ofthe target surface within the intra-oral cavity.

The system 50 is typically located at a dental clinic, and may be linkedto one or more service centers 23 and/or dental labs 26, via acommunication means or network such as for example the Internet or othersuitable communications medium such as an intranet, local accessnetwork, public switched telephone network, cable network, satellitecommunication system, and the like, indicated by the cloud at 24.Optionally, it is also possible for some dental labs 26 to be linked toeach other, via the same one or a different one of said communicationmedium, for example when such dental clinics or labs form part of acommon commercial entity. Further optionally, such interlinked dentallabs 26 may be further linked with other entities, for example a headclinic or head lab, comprising a centralized data base (not shown).

Typically, the design and manufacture of dental prosthesis may beeventually carried out at the dental lab 26 or at the service centre 23,or alternatively one or both of these activities may be shared betweenthe two; in each case the design and manufacture are preferably based onthe original 3D data of the oral cavity previously obtained. Thus,exchange of data between the system 50 and the dental lab 26 and/orservice center 23 may be useful in creating an optimal geometry for apreparation being made in the intraoral cavity that enables the bestprosthesis to be designed therefor, for example.

Alternatively, scanning of the dental cavity to provide the 3D data maybe accomplished using a suitable apparatus, for example as disclosed inany one of U.S. Pat. Nos. 4,837,732, 4,611,288, 6,594,539, 6,402,707,6,364,660, U.S. Patent Publication No. 2002/0028418, U.S. PatentPublication No. 2002/0058229, U.S. Pat. Nos. 5,652,709, 4,575,805,5,733,126, 5,880,962, 4,742,464, 4,663,720, WO 02/071306 mutatismutandis. The contents of these publications are incorporated herein intheir entirety by reference thereto.

The 3D data obtained by the probe may then be stored in a suitablestorage medium, for example a memory in a computer workstation, forfurther processing, as described herein.

Alternatively, a negative cast or impression is taken of the patient'steeth, in a manner known in the art, and this negative model and apositive cast is made from this model suitable for scanning. Thepositive cast may be scanned by any method known in the art, includingusing the aforesaid probe manufactured under the name of PROSTHOCAD oras disclosed in WO 00/08415. Alternatively, the negative model itselfmay be scanned.

Alternatively, a composite positive-negative model may be manufacturedfrom the original negative model. Thereafter, the positive-negativemodel may be processed to obtain 3D digitized data, for example asdisclosed in U.S. Pat. No. 6,099,314, assigned to the present assignee,and the contents of which are incorporated herein in their entirety.

Alternatively, the 3D digitized data may be obtained in any othersuitable manner, including other suitable intra oral scanningtechniques, based on optical methods, direct contact or any other means,applied directly to the patient's dentition or to a physical modelthereof previously obtained. Alternatively, X-ray based, CT based, MRIbased, or any other type of scanning of the patient's infra-oral cavity,or of a physical model thereof previously obtained, may be used. Thephysical model may be a positive model or a negative model of thedentition, and is obtainable using methods known per se in the art.

The additional 3D data that relates to the patient's dentition includes,inter-alia, information relating to the surrounding of the tooth to berestored, e.g. 3D representation of the patient's dentition, includingthe upper and lower jaws and their occlusion relationship. Suchinformation is needed, e.g. for the design of the dental crown, and canbe generated for example, as disclosed in U.S. Pat. Nos. 6,099,314 and6,334,853.

Typically, the 3D digitized data W is obtained in a manner such thatenables the data to be procured from the patient and analyzed accordingto the invention during a regular visit of a patient to a practitioner.

Optionally, the numerical entity or 3D digitized data W may furthercomprise a fourth prime independent variable, relating to a colorparameter that is expressed numerically and is associated with thespatial coordinates. The color parameter may itself be comprised ofindependent prime color variables—for example relating to the red, blueand green (RGB) components associated with the color parameter.Alternatively, the color parameter may be expressed in terms of the Hue,Saturation and Intensity (HIS). Alternatively, any other color parametermay be used, including parameters that provide a measure of internalreflectance and translucency, or any other optical property of teeth.Thus, such a numerical entity typically comprises a data set having aplurality of 4-dimensional arrays—(x, y, z, c), wherein each arrayrepresents the x, y, z, geometrical coordinates, and wherein crepresents the color value, of a point on a surface within theintra-oral cavity. Any suitable means may be used to provide thisnumerical entity. For example, a three-dimensional surface scanner withcolor capabilities may be used. Thus, advantageously, such a scannermakes use of confocal imaging for providing an accuratethree-dimensional representation of the target surface within theintra-oral cavity. Color values may then added to each data point ofthis data set by obtaining a two-dimensional color image of the targetsurface, and then mapping the color values of the two-dimensional imageonto the three-dimensional “image”, for example as described incopending applications assigned to the present assignee, U.S.provisional Patent Application No. 60/580,109, entitled “METHOD FORPROVIDING DATA ASSOCIATED WITH THE INTRAORAL CAVITY”, and U.S.provisional Patent Application 60/580,108, entitled “METHOD ANDAPPARATUS FOR COLOR IMAGING A THREE-DIMENSIONAL STRUCTURE”. Thesereferences are incorporated herein in their entirety by referencethereto.

In Step 130, the 3D virtual model W is manipulated to obtain digitalrepresentations of certain areas of interest in the oral cavity 10 forthe design of the crown prosthesis, including the finish line 84,shoulder 85 and external surface 86 of the preparation 12.

Analysis of the 3D model W of the preparation in the intra oral cavitymay be conducted, for example, by the dental lab 26, which typicallycomprises a laboratory, or a design or manufacturing entity that mayprovide direct technical services to the dental clinic in which thesystem 50 may be located. The location of the finish line 84 may belocated using a suitable method and system, for example, as disclosed inU.S. patent application Ser. No. 10/623,707 and WO 04/008981, alsoassigned to the present assignee, and the contents of which areincorporated herein in their entirety. Alternatively, the finish linemay be generated using methods disclosed in U.S. Pat. No. 5,266,030 thecontents of which are incorporated herein. The virtual generation of thefinish line may be incorporated as an integral component in the methodof the invention.

Alternatively, the finish line 84 may be located in the 3D model W usingany other means, including manual, automatic, interactive or any othermeans, or a combination of such means. Similar methods may be employedfor defining the shoulder 85 (where appropriate, depending on the formof the finish line), and for defining the outer surface 86 of thepreparation 12.

In step 140, the prosthesis geometry is designed. The prosthesis maycomprise a single layer, or alternatively be multi-layered.

Referring to FIG. 6, a virtual representation of such a crown, generallydesignated 20, is in the form of a cap 180 that is fitted onto a coping160. The virtual coping 160 can be designed, and a real coping based onthis design can be manufactured, using any suitable method. One suchsuitable manufacturing method is disclosed in copending applicationsU.S. patent application Ser. No. 10/814,653 and in PCT/IL2004/000290,entitled “METHOD AND SYSTEM FOR FABRICATING A DENTAL COPING, AND ACOPING FABRICATED THEREBY”, also assigned to the present Assignee. Thecontents of these references are incorporated herein in their entiretyby reference thereto.

The coping 160 is typically made from a metal, ceramic or other verystrong material, and is designed for taking the mechanical loads of thecrown 20 associated with the normal activity of the teeth. The innersurface 161 and lower edge 162 of the coping 160 need to closely matchthe preparation 12 and finish line 84/shoulder 85, and moreover providea reasonable insertion path for the crown 20. Typically, the fittingtolerance for the internal surface 161 and lower edge 162 needs to be inthe order of about 40 microns or less, which is more demanding than forthe cap 180. Typically, if the dimensional accuracy is not maintained tothis tolerance level, there may be a risk of infection of the remainingparts of the tooth, the infection entering via the gap between the crownand the preparation, in particular between the lower edge 162 and thefinish line 84. Furthermore, where such tolerances are not met, the lifeof the prosthesis may be severely reduced. Although prior art dentallabs do design and manufacture copings, such close tolerances are nottypically achievable by most regular dental labs that currently providesuch services to clinics. Accordingly, the design and manufacture of theinternal surface 161 and lower edge 162 may be advantageously carriedout in the present invention by the service centre 23, which generallyhas the equipment to do so. By centralizing such specialized andaccurate work from a number of clinics 22, the service center 23 is ableto carry out such work in a more cost effective and efficient manner,and generally more accurately, than the dental lab 26.

Optionally, the processor 52 also has suitable software to define theinner surface 161 according to predetermined parameters. Theseparameters take into account the geometries of the external surface ofthe preparation 12 including finish line 84 and shoulder 85, the spacingrequired between the coping 160 and the preparation 12 to accommodatethe adhesive or cement that is used to provide the bond between the two.The processor 52 may also comprise suitable software to provide theexternal shape of such a coping 160, and thus provide a completegeometrical representation or 3D data of the coping 160, digitally. Theexternal surface 163 of the coping 160 may be defined in any number ofways. Typically, at least a majority of the external surface of thestump 82 is displaced from the internal surface thereof by a uniformamount to provide an approximately constant thickness throughout.However, the thickness of the coping 160 may vary for a number ofreasons. For example, it may be necessary in some cases to provide acoping that is stronger in some parts than in others, reflecting theactivity that the crown 20 will be expected to engage in—as a molar,incisor, canine and so on.

The cap 180, which may be formed from a single layer or from a pluralityof partially or fully overlapping generally concentric layers, forexample three layers 21, 22, 23, preferably has a natural lookingappearance. Further, the dimensions of the crown 20, in particular thedefinition of the external surface 28 thereof depends on externalfactors and needs to be such as to enable the crown 20 to fit betweenthe adjacent teeth A, B (FIG. 3). Of course, the number of layers andthe extent of overlapping between each successive layer will generallyvary from one prosthesis to another. Further, the external surface 28 isdefined such as to provide adequate occlusion with the “working side” ofthe tooth and avoiding interfering contact between the crown 20 andteeth of the opposite jaw, in particular the opposing tooth D, when thecrown is fixed onto the corresponding preparation 12 in the intraoralcavity 10.

An outer shape for the external surface 28 may be chosen in a number ofways. For example, if the original tooth that the crown 20 is replacingis still available, and the outer surface thereof is of a reasonableform, this original tooth may be scanned and the 3D data of the surfaceobtained. If necessary, this 3D data may be considered as a startingpoint, and the final shape of the external surface 28 is obtained bymanipulating this data as required by the technician or other user thatis designing the surface 28. Alternatively, if the patient has areasonably healthy tooth on the same jaw but on the adjacent quadrant ata position corresponding to where the crown is to be fitted, the 3D dataof the surface of this tooth is obtained. Optionally, this tooth may bescanned as described herein to obtain the 3D spatial coordinatesthereof, unless this data may already be available from the 3D data ofthe oral cavity 10 stored in the processor 52. Typically, such 3D-datawould need to be transformed to provide a lateral inversion of thecoordinates, suitable for a prosthesis in the other half of the jaw.Alternatively, a suitable profile for surface 28 may be chosen andobtained from a library 35 (FIG. 5) that comprises the 3D spatialprofiles of shapes or profiles of the outer surfaces of a plurality ofcrowns and teeth. If necessary the relative size and shape of thesurface 28 may be adjusted by the user to better match the other teethin the jaw. Then, the chosen surface is adjusted in any suitable manner,either manually, automatically, interactively or in any other manner, inorder that the required target dimensions of surface 28 will fit withina control volume that defines the maximum dimensions of the crown 20, asrequired to conform to the space available in the intra oral cavity 10.In particular, the control volume may be chosen such as to provideadequate clearance between the crown and adjacent teeth, and adequateocclusion with the opposite teeth, when the crown 20 is properly fixedonto the preparation 12. A virtual representation C₀ of the externalsurface 28 is then defined.

In cases where the cap 180 comprises a number of layers, such as forexample layers 21, 22, 23, the internal surface 29 of the virtual cap180 is typically first defined, and the internal surface issubstantially complementary to the external surface 163 of the coping160. Accordingly, the 3D structure of the internal surface 29 may beobtained from the external surface 163, as described above, for example.Alternatively, if the real coping, that is, the physical coping, alreadyexists, the external surface thereof can be directly scanned, forexample in a similar manner to that described herein for the intraoralcavity, mutatis mutandis. If such an option is chosen, then the realcoping may be scanned while fitted onto the preparation, and in factStep 120 may be conducted with the coping in place on the preparation.Once the internal surface 29 and the external surface 28 are defined invirtual space, the characteristics of the internal layers 21, 22, 23 canbe defined, taking into account the material from which thecorresponding real, physical layers are to be made, according to anysuitable rules and/or experience known to the user, to provide virtual3D definitions C₁, C₂ of the external surfaces 25, 26, respectively, ofinternal layers 21, 22, respectively. The external surface of theoutermost layer is the external surface 28 of the cap 180. The opticalproperties as well as the mechanical strengths of these materials arefactors typically considered when designing the internal layers, as wellas the shading desired for the crown 20. To assist in this process,shading data for the crown 20 may be obtained using the method disclosedin U.S. provisional Patent Application No. 60/580,109 entitled “METHODFOR PROVIDING DATA ASSOCIATED WITH THE INTRAORAL CAVITY”, also assignedto the present Assignee. The contents of this reference are incorporatedherein in their entirety by reference thereto. Each of the internallayers 21, 22, and/or the external layer 23 may be full layers, coveringcompletely the layer immediately below them including the coping, or mayonly partially cover inner layers and/or coping, for example comprisingislands of material formed on the coping or an inner layer. Fullflexibility as to the extent, thickness, and material of each layer isprovided, enabling the strength of the prosthesis to be maximized whileallowing the same to have a natural looking appearance that suitablymatches other teeth of the intra oral cavity. In other embodiments, thecrown 20 may be single-layered, and thus only the external surface 28needs to be defined.

The design of the external surface 28, and where appropriate of theexternal surfaces 25, 26 (and optionally of the internal surface 161)may be executed by the processor 52 at the dental clinic, for example,or alternatively at the service center 23, or at the dental lab 26. Ifat the latter, and if use is made of a library of 3D spatial profiles ofshapes or profiles of the outer surfaces of a plurality of crowns andteeth, and optionally also design rules for the internal layers, thenthe dental lab 26 can make use of library of the service centre 23, viacommunications network 24. Similarly, if the design is carried out atthe dental clinic, the processor 52 may also make use of the library ofthe service centre 23, via communications network 24. Alternatively, thesystem 50 may have its own digital library 35 of 3D spatial profiles ofshapes or profiles of the outer surfaces of a plurality of crowns andteeth, operatively connected to a processor 52 or other computer, asillustrated in FIG. 5, which comprises display 54 and user interface 59such as a mouse and/or keyboard.

In Step 150, the processor 52 converts 3D data C₀, C₁, C₂ representativeof the external surface 28 of the crown, and of the external surfaces25, 26 respectively, into a set P of CNC instructions P₀, P₁, P₂ formachining the corresponding layers of wax, according to the methoddescribed in more detail below. Alternatively, the processor 52 sendsthe aforesaid 3D data to another processor 53, for example via network24, that is particularly adapted for providing CNC instructions. In anycase, the CNC instructions are then sent to a manufacturing center 60directly or via network 24. Alternatively, the CNC instructions may bestored in any storage medium, for example magnetic tape, optical disk,and so on, and the medium physically sent to the manufacturing center 60to be read and processed thereat.

Referring to FIG. 7, the manufacturing center 60 comprises an inputfacility 61 for receiving the set P of CNC data, for example via network24 or via a physical storage medium, a processor 62, which processes theCNC data, and a machining center 65 that carries out a material removaloperation on a workpiece based on CNC set of instructions P processed bythe processor 62 to produce solid replicas in wax corresponding to the3D data C₀, C₁, C₂.

Optionally, the manufacturing center 60, or indeed some othermanufacturing center (not shown) may be adapted for producing a coping160 directly from a suitable hard material, using the machininginstructions, or indirectly via a lost wax process, for example asdisclosed in the aforesaid applications entitled “METHOD AND SYSTEM FORFABRICATING A DENTAL COPING, AND A COPING FABRICATED THEREBY”.Alternatively, the coping 160 may be provided by means, indicated at 69,external to the manufacturing center 60.

The machining center 65 comprises any suitable machining tool that isadapted for material removal, and may include inter alia mechanicaltools such as drills for example, laser tools such as for example laserdrills or cutters, ultrasonic tools such as for example ultrasoniccutters, and so on. The machining paths and material removalcharacteristics of such tools can be finely controlled, typically by acontrol computer such as processor 62 comprised in or operativelyconnected to said machining center 65.

Operation of the manufacturing center 60, according to variousimplementations of the method of the invention, will now be described ingreater detail with reference to FIG. 2.

In the first exemplary implementation of the method of the invention,and referring to FIGS. 2 and 8 a to 8 h, the method 200 is adapted forthe fabrication of a multi-layered crown prosthesis 20. In this example,the prosthesis 20 comprises two internal layers over the coping, plus anouter layer, corresponding to layers 21, 22, 23 of the virtual modeldescribed above, but may be extended to prostheses having a greaternumber of full or partial layers in a similar manner to that described,mutatis mutandis. In step 210 of the method, a coping 160 is provided,substantially as described above.

Referring to FIG. 8a , in step 220, a wax layer 90 is applied to theexternal surface 163 of the coping. The wax layer 90 is sufficientlylarge so that it completely encloses the geometry defining the externalsurface 25 of the innermost virtual layer 21.

The set of wax models on the coping are made of relatively hard, durablewax or similar material. In particular, each wax model is made from amaterial that on the one hand lends itself to milling in a millingmachine, while on the other hand has a low melting point and aftermelting, it has a kinematic viscosity sufficiently low to be usable in alost wax technique known per se in the art of metal casting. Preferably,such a material has a melting point and congealing point of about 55° C.to about 80° C. and a kinematic viscosity of less than 90 m² sec. atabout 100° C.

In Step 230 the machining center 65 then processes the CNC instructionsP₂ corresponding to surface 25 (received at Step 150), applying amaterial removal operation to the wax layer 90 to remove all the wax 90Aoutside of the envelope represented by surface 25. Thus, a suitablemilling or other machining process, for example, may be applied to theexternal surface of the wax layer. The remaining wax layer 90B after thematerial removal process is a physical wax model of layer 21 mounted onthe coping 160.

In Step 240, the wax layer 90B is invested in a material that solidifiesonto the external side of the wax layer (still on the coping) and formsa mold 95A (FIG. 8b ). Typically, access to the wax layer 90A isprovided by means of a channel (not shown), for example.

Referring to FIG. 8b , and in Step 250, the combination provided in Step240 is heated such that the wax layer 90B is burnt out, leaving a cavity98A into which the innermost crown layer 99A may be cast. The burnt-outwax may be removed via the aforesaid channel, for example.

In Step 260—the innermost crown layer 99A is fabricated in the cavity98A in any suitable way, for example by injecting a suitable moltenmetal into cavity 98A, and after hardening, the mold 95A is removed fromthe metal casting to provide a metal layer 99A.

Alternatively, such a lost wax process described with reference to Steps240 to 260 may be based on a process used for the production ofrestorations as described by Ivoclar Vivadent Ltd. regarding the IPSEmpress system in http://www.ivoclarco.uk/technician/nonmetal2.html,mutatis mutandis, for example. Essentially, the after the wax layer 90Bis ready (mounted onto the coping), it is invested, and a leucite orlithium disilicate subframe, created through the IPS Empress system.These structures are then layered with leucite (for leucitesub-structure) or fluorapatite ceramic (over lithium disilicateframework) and then fired in the conventional ceramic furnace.

Alternatively, a suitable ceramic molding composition may be pressedinto the cavity 98A, for example in a manner similar to that disclosedin U.S. Pat. No. 6,126,732, mutatis mutandis, the contents of which areincorporated herein in their entirety. Alternatively, sintering methodsmay be applied to the mold to produce a ceramic inner layer 99A. In eachcase, the mold 95A may have to be modified according to the details ofthe particular process used—for example, the mold may be divided intotwo or more parts that fit together to provide said cavity 98A.

In any case, a suitable method is used for providing a layer of crownmaterial 99A based on the CNC machined layer of wax 90B.

In Step 270, if this was the last layer required for the crown, Step 290is implemented, otherwise, another layer is fabricated on the crown,continuing with Step 280. Since layer 99A is only the first of threelayers for this particular example, the method of the inventionaccording to this embodiment continues with step 280, and referring toFIG. 8c , a second wax layer 91 is applied, in a similar manner to thatdescribed above for Step 220 mutatis mutandis, but this time over thecrown layer 99A rather than the coping 160. Of course, if the crownlayer 99A only partially overlapped the coping, leaving parts of thecoping exposed, then the new wax layer may, depending on the geometry ofthe second layer of the prosthesis, also overlap these exposed parts ofthe coping. Thus, the wax layer 91 is sufficiently large so that itcompletely encloses the geometry defining the external surface 26 of thenext innermost virtual layer 22. Now, in Step 230, the machining center65 then processes the CNC instructions P1 corresponding to surface 26(received at Step 150), applying a material removal operation to the waxlayer 91 to remove all the wax 91A outside of the envelope representedby surface 26. The remaining wax layer 91B is a physical wax model oflayer 22 mounted on the coping previously fabricated crown layer 99A. InStep 240, the wax layer 91B is invested to form a mold 95B (FIG. 8d ),and in Step 250, cavity 98B is formed into which the next crown layer99B may be formed in Step 260, substantially as described for the firstlayer 99A, mutatis mutandis (FIG. 8e ).

As there is still another layer to be added, Step 270 is followed byanother cycle commencing at Step 280, wherein, referring to FIG. 8f , athird wax layer 92 is applied, in a similar manner to that describedabove for Step 220 mutatis mutandis, but this time over the second crownlayer 99B rather than the first crown layer 99A or the coping 160. Ofcourse, if the crown layer 99B only partially overlapped the first crownlayer 99A and/or the coping, leaving parts of the crown layer 99A and/orcoping exposed, then the new wax layer will, depending on the geometryof the second layer of the prosthesis, also overlap these exposed partsof the crown layer 99A and/or coping. Thus, the wax layer 92 issufficiently large so that it completely encloses the geometry definingthe external surface 28 of the crown. Now, in Step 230, the machiningcenter 65 then processes the CNC instructions P₀ corresponding tosurface 28 (received at Step 150), applying a material removal operationto the wax layer 92 to remove all the wax 92A outside of the enveloperepresented by surface 28. The remaining wax layer 92B is a physical waxmodel of layer 23 mounted on the previously fabricated crown layer 99B.In Step 240, the wax layer 92B is invested to form a mold 95C (FIG. 8g), and in Step 250, cavity 98C is formed into which the final crownlayer 99C may be formed in Step 260, substantially as described for thefirst layer 99A or second layer 99B, mutatis mutandis (FIG. 8h ).

At this stage, in Step 270 it is determined that this is the final layerfabricated according to the process of the invention, and the processends at 290.

Alternatively, the final layer 99C of the crown may be built onto theprevious layers 99B and 99A using manual (traditional) methods known perse in the art. In such a case, at the end of the second fabricationcycle, wherein the second layer 99B is completed, Step 270 is followedby Step 290, and then by a manual step (not shown) of preparing thefinal layer 99C.

In a second exemplary implementation of the method of the invention, andreferring to FIGS. 2 and 9 a to 9 c, the method 200 is adapted for thefabrication of a single-layered crown prosthesis 20′. In this example,the prosthesis 20′ comprises a single outer layer over the coping,corresponding to a combination of layers 21, 22, 23 of the virtual modeldescribed above, but without the interfacing surfaces 25, 26. In step210 of the method, a coping 160 is provided, substantially as describedabove.

In Step 220 a wax layer 94 is applied onto the coping 160, sufficientlylarge so that it completely encloses the geometry defining the externalsurface 28. In Step 230, the machining center 65 then processes the CNCinstructions P₀ corresponding to surface 28 (received at Step 150),applying a material removal operation to the wax layer 94 to remove allthe wax 94A outside of the envelope represented by surface 28. Theremaining wax layer 94B is a physical wax model of cap 180 mounted onthe coping. In Step 240, the wax layer 94B is invested to form a mold 95(FIG. 9b ), and in Step 250, cavity 98 is formed into which the cap 180in the form of crown layer 99 may be formed in Step 260, substantiallyas described for the first example above, mutatis mutandis (FIG. 9c ).At this stage, in Step 270 it is determined that this is the final layerfabricated according to the process of the invention, and the processends at 290.

In a third exemplary implementation of the method of the invention, andreferring to FIGS. 2 and 10 a to 10 e, the method 200 is adapted for thefabrication of a double-layered bridge prosthesis 220. In this example,the prosthesis 220 comprises one internal layers over a pair of spacedcopings, 212, 214, plus an outer layer, and these layers span twoabutment teeth having a single pontic therebetween. Nevertheless, thisapplication of the method may be extended to prostheses having a greateror lower number of layers, and to a greater number of pontics and/orconnectors, for example in a similar manner to that described, mutatismutandis.

The fabrication of the bridge prosthesis according to the invention ispreceded by the definition of CNC material removing instructions foreach layer of the prosthesis (Step 150), and typically this isaccomplished in a similar manner to that described above for the crownprosthesis, mutatis mutandis. Thus, the intraoral cavity 10′ is scannedto provide a 3D virtual model thereof, and this is manipulated andprocessed to provide a virtual model of the external surface of theprosthesis, a virtual model of the interface surface between theinternal and external layer of the bridge (i.e., the external surface ofthe inner layer), CNC instructions corresponding to these two surfaces,and a pair of real copings 262, 264.

Thus, in step 210 of the method according to this embodiment, a pair ofcopings 262, 264 provided, each similar to the coping 160 substantiallyas described above, mutatis mutandis. The copings 262, 264 are adaptedto fit onto preparations 212, 214, respectively, of the dental site(FIG. 4).

Referring to FIG. 10a , in Step 220 a wax layer 291 is applied onto thetwo copings 262, 264, this layer being sufficiently large so that itcompletely encloses the geometry defining the internal layer of thebridge 220. Advantageously, the spatial relationship between the twocopings 262, 264, in relation to their mounting positions andorientations in the intraoral cavity 10′ (FIG. 4), is maintained bytemporarily mounting the copings onto a holder 250, illustrated in FIG.11. The holder 250 comprises a pair of seats 252, 254 which compriseexternal surfaces substantially identical to the external surfaces ofthe preparations 212, 214, respectively, and moreover are spaced andoriented with respect to one another to mimic the spacing andorientation of the real preparations 212, 214 with respect to theintraoral cavity 10′. The holder 250, and in particular the seats 252254 may be manufactured via a CNC machining operation based on thevirtual model obtained in step 120 of the preprocess 100.

In Step 230, the machining center 65 then processes the CNC instructionscorresponding to external surface 226 of the internal layer (received atStep 150), applying a material removal operation to the wax layer 291 toremove all the wax 291A outside of the envelope represented by surface226. The remaining wax layer 291B is a physical wax model of internallayer mounted onto the two copings 262, 264. In Step 240, the wax layer291B is invested to form a mold 295A (FIG. 10b ), and in Step 250,cavity 298A is formed into which the bridge layer 299A may be formed inStep 260, substantially as described for the first example above,mutatis mutandis.

As there is still an outer layer to be added, to complete theprosthesis, Step 270 is followed by a second cycle commencing at Step280, wherein, referring to FIG. 10c , a second wax layer 292 is applied,in a similar manner to that described above for Step 220 mutatismutandis, but this time over the inner bridge layer 299A rather than thecopings 262, 264. Thus, the wax layer 292 is sufficiently large so thatit completely encloses the geometry defining the external surface 228 ofthe bridge. Now, in Step 230, the machining center 65 then processes theCNC instructions corresponding to surface 228 (received at Step 150),applying a material removal operation to the external wax layer 292, forexample external maching (e.g. milling) of the wax layer, to remove allthe wax 292A outside of the envelope represented by surface 228. Theremaining wax layer 292B is a physical wax model of the final bridgelayer mounted on the previously fabricated bridge layer 299A. In Step240, the wax layer 292B is invested to form a mold 295B (FIG. 10d ), andin Step 250, cavity 298B is formed into which the final bridge layer 29Bmay be formed in Step 260, substantially as described for the firstlayer 299A, mutatis mutandis (FIG. 10e ).

At this stage, in Step 270 it is determined that this is the final layerfabricated according to the process of the invention, and the processends at 290.

Alternatively, the final layer 299B of the bridge prosthesis may bebuilt onto the previous layer 299A using manual (traditional) methodsknown per se in the art. In such a case, at the end of the firstfabrication cycle, wherein the first layer 299A is completed, Step 270is followed by Step 290, and then by a manual step (not shown) ofpreparing the final layer 299B.

Optionally, it is possible to join the copings 262, 264 via a connector,or indeed a pontic. This may be done after the copings are produced, oras part of the production process. For example, wax replicas of suitableconnectors and/or one or more pontics are made, either manually or byany suitable method, including machining, casting and so on, and thenthe connectors and/or pontics are joined to the wax copings of theabutment teeth in a suitable manner, for example as is known in the artper se. The metal or ceramic structure for the bridge is then made fromthe wax model thereof in a similar manner to that disclosed in theaforesaid application entitled “METHOD AND SYSTEM FOR FABRICATING ADENTAL COPING, AND A COPING FABRICATED THEREBY”. In any case, theconnectors and/or pontics hold the two copings in their appropriatespatial relationships, and the method of the invention is then appliedto the resulting structure in a similar manner to that described abovefor the bridge prosthesis, mutatis mutandis.

The invention is not bound by the specified example of FIGS. 8a to 11and, accordingly, other scenarios may be used in addition or in lieu ofthe above, depending upon the particular application. Specifically, theinvention can also be utilized in a less “digitized” scenario, forexample one in which the care provider gathers the relevant informationrelating to the patient's dentition in a non-digitized manner (e.g. bytaking a physical impression of the patient's dentition), and thepatient's dentition data is digitized later on, at a laboratory.

Referring again to FIG. 5, the dental lab 26 is typically characterizedas being equipped or otherwise able to design part or whole prostheses,and/or to partially manufacture or assemble the same, particularly whereclose tolerances are relatively less critical. On the other hand, whilethe service center 23 may also be equipped to design part or wholeprostheses, and/or to fully or partially manufacture and/or assemble thesame, it is particularly suited to do any of these activities whereclose or tight tolerances are in fact critical and/or difficult toachieve.

While the service centre 23 and dental labs 26 may be located in adifferent geographical zone to the dental clinic, for example, differentcountries, different cities in the same country, different neighborhoodsin the same city, or even different buildings in the same neighborhood,they may also be housed in the same building, and in any case maintaintheir separate functions and capabilities, as described herein.

The system 50 may also be linked to one or more consultation centers 27,also via network 24, wherein such consultation centers 27 may comprisedental experts, for example, that may provide feedback to the user ofsystem 50, based on data transmitted therefrom to the centers 27,according to the invention.

The invention allows to gather the 3D data that represents the patient'sdentition in one place (say, the care provider's clinic), to design thevirtual prosthesis model at the clinic or at a remote location, togenerate the CNC set of instructions at another place and to fabricatethe wax prosthesis at a yet another location. Furthermore, the inventionallows for the fabrication of the wax layers and the prosthesis layersat different locations without damaging the quality of the prosthesislayers due to deformations in the wax models. It should be noted thatadditional, intermediate steps in which digital data is transmittedbetween remote locations might be carried-out as part of method of theinvention.

The dental prosthesis manufactured according to the present invention isthus derived from a set of wax models, which due to the relativelysoftness of each model can be machined to a smoother surface texturethan is possible when machining the prosthesis directly from the desiredfinal material such as metal or a ceramic. Accordingly, dentalprostheses produced using the method of the invention using the wax forpreparing a mold are correspondingly smoother, and furthermore it ispossible to include fine details in each layer, with respect toprostheses produced using direct material removal methods applied to thefinal material.

Furthermore, the wax-based method of the present invention for producingthe dental prostheses has some advantages over direct material removalmethods that are used elsewhere for producing the prostheses directlyfrom the desired final material. For example less wear and breakage areexperienced by the machining tool, and thus lowers costs. Furthermore,deformations of the tool, when a direct contact tool such as for examplea mechanical tool is used, is less likely, and thus less deviations fromthe nominal dimensions of the coping with respect to the virtual modelthereof occur than when producing a coping directly from a metal orother hard material.

In the method claims that follow, alphanumeric characters and Romannumerals used to designate claim steps are provided for convenience onlyand do not imply any particular order of performing the steps.

Finally, it should be noted that the word “comprising” as usedthroughout the appended claims is to be interpreted to mean “includingbut not limited to”.

While there has been shown and disclosed exemplary embodiments inaccordance with the invention, it will be appreciated that many changesmay be made therein without departing from the spirit of the invention.

1-15. (canceled)
 16. A method for manufacturing a dental prosthesis,comprising: generating a three-dimensional virtual model of a dentalprosthesis comprising a first virtual prosthesis layer including a firstvirtual external surface and a second virtual prosthesis layer includinga first virtual internal surface, the first virtual internal surfacebeing substantially complementary to the first virtual external surface;producing a first wax model, corresponding to the first virtualprosthesis layer, the first wax model being produced by materialoperations to form a first external surface of the first wax model thatcorresponds to the first virtual external surface, the materialoperations being based on the three-dimensional virtual model; producinga second wax model, corresponding to the second virtual prosthesislayer, the second wax model being produced by material operations toform a first internal surface of the first wax model that corresponds tothe first virtual internal surface, the material operations being basedon the three-dimensional virtual model; and producing the dentalprosthesis based on the first wax model and the second wax model. 17.The method according to claim 16, wherein producing the second wax modelcomprises forming the second wax model on the first wax model.
 18. Themethod according to claim 16, wherein the second virtual prosthesislayer includes a second virtual external surface and producing thesecond wax model includes producing by material operations a secondexternal surface of the second wax model that corresponds to the secondvirtual external surface.
 19. The method according to claim 16, whereinthe dental prosthesis is a multi-layered bridge prosthesis, wherein thefirst and second wax models form a composite wax model of the dentalprosthesis substantially corresponding to the three-dimensional virtualmodel.
 20. The method according to claim 16, wherein the dentalprosthesis is a bridge prosthesis and the first virtual prosthesis layerincludes second and third virtual internal surfaces, the second andthird virtual internal surfaces substantially complementary to acorresponding external surface of a first and a second coping.
 21. Themethod according to claim 16, wherein the dental prosthesis is amulti-layered bridge prosthesis, wherein the set of first and second waxmodels each comprises a wax model of a respective layer of the dentalprosthesis substantially corresponding to virtual prosthesis layerscreated in the three-dimensional virtual model.
 22. The method accordingto claim 16, wherein generating the three-dimensional virtual model ofthe dental prosthesis comprises providing a three-dimensional digitaldata relating to the patient's dentition, the three-dimensional digitaldata including data representative of surface topology of a preparationand its surroundings.
 23. The method according to claim 22, wherein thematerial operations are material removal operations.
 24. The methodaccording to claim 23, wherein three-dimensional digital data isgenerated using an optical scanner and the optical scanner comprises aprobe for determining a three-dimensional structure by focusing of anarray of light beams.
 25. The method according to claim 22, whereingenerating the three-dimensional virtual model of the dental prosthesisis performed directly on an intraoral cavity comprising the preparation.26. The method according to claim 16, wherein producing the dentalprosthesis includes producing a dental prosthesis on a first coping. 27.A system for manufacturing a dental prosthesis, comprising: a processor;and memory comprising instructions that when executed by the processor,cause the system to: generate a three-dimensional virtual model of thedental prosthesis comprising a first virtual prosthesis layer includinga first virtual external surface and a second virtual prosthesis layerincluding a first virtual internal surface, the first virtual internalsurface being substantially complementary to the first virtual externalsurface; produce a first wax model, corresponding to the first virtualprosthesis layer, the first wax model being produced by materialoperations to form a first external surface of the first wax model thatcorresponds to the first virtual external surface, the materialoperations being based on the three-dimensional virtual model; produce asecond wax model, corresponding to the second virtual prosthesis layer,the second wax model being produced by material operations to form afirst internal surface of the first wax model that corresponds to thefirst virtual internal surface, the material operations being based onthe three-dimensional virtual model; and produce the dental prosthesisbased on the first wax model and the second wax model.
 28. The systemaccording to claim 27, wherein producing the second wax model comprisesforming the second wax model on the first wax model.
 29. The systemaccording to claim 27, wherein the dental prosthesis is a multi-layeredcrown prosthesis, wherein the first and second wax models comprises awax model of the first and second layer of the prosthesis substantiallycorresponding to first and second virtual prosthesis layers generated inthe three-dimensional virtual model.
 30. The system according to claim27, wherein the dental prosthesis is a multi-layered bridge prosthesis,wherein the first and second wax models form a composite wax model ofthe dental prosthesis substantially corresponding to thethree-dimensional virtual model.
 31. The system according to claim 30,wherein the dental prosthesis is a bridge prosthesis and the firstvirtual prosthesis layer includes second and third virtual internalsurfaces, the second and third virtual internal surfaces substantiallycomplementary to a corresponding external surface of a first and asecond coping.
 32. The system according to claim 27, wherein the dentalprosthesis is a multi-layered bridge prosthesis, wherein the set offirst and second wax models each comprises a wax model of a respectivelayer of the dental prosthesis substantially corresponding to virtualprosthesis layers created in the three-dimensional virtual model. 33.The system according to claim 28, wherein generating thethree-dimensional virtual model of the dental prosthesis comprisesreceiving a three-dimensional digital data relating to the patient'sdentition, the three-dimensional digital data including datarepresentative of surface topology of a preparation and itssurroundings.
 34. The system according to claim 32, wherein thethree-dimensional digital data is generated using an optical scanner.35. The system according to claim 33, wherein generating thethree-dimensional virtual model of the dental prosthesis is performeddirectly on an intraoral cavity comprising the preparation.